JPS59133564A - Controlling method of electrophotographic image - Google Patents

Abstract

PURPOSE:To obtain a good copy free from ground soil and lengthen interval of maintenance by detecting the quantity of adhesion of toner on the surface of low potential part of a photosensitive body and on the surface of reference potential part, comparing the two, and adjusting developing bias and amount of exposure to conform the two. CONSTITUTION:The amount of adhesion of toner on the surface of low potential part corresponding to detected pattern 16 of a photosensitive drum 1 on which a little toner is adhering and the amount of adhesion of toner on the surface of reference potential part on which little tonr is adhering are detected from reflection factor of the light by a photo-sensor unit 5. The detected value is reduced to about 1/5 by division of resistances 20, 21, and inputted to a controlling circuit 23 through an A/D converter 22. A developing bias power source 24 is driven by the controlling circuit 23 to conform the two input. By this way, a good copy free from ground soil can be obtained, and interval of maintenance can be lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electrophotographic image control method, particularly an image control method of a type that prevents background smear on a copy by controlling the exposure amount and/or the developing bias voltage value. Regarding.

(Prior Art) As is well known, in electrophotography, an original image is reproduced by charging, exposing, and developing the surface of a photoreceptor having a photoconductive insulating layer. To explain the general characteristics of such electrophotography with reference to Fig. 1, first, as is clear in the The amount of exposure of the photoreceptor corresponding to the area is small, and the amount of exposure of the photoreceptor corresponding to the low-density non-image area or background area of the document is large. As is clear from the quadrant (2), as the exposure amount of the photoreceptor increases, the surface potential of the photoreceptor decreases, and as shown in the quadrant (2), when the surface potential of the photoreceptor decreases, the density of the developed image decreases. If we limit this relationship to the area other than the text area of the original, that is, the background area, if the background area is pure white, the original density will be the lowest, so the photoreceptor exposure will be the maximum, and the photoreceptor surface potential will be the lowest, and the developed image density will be the lowest. It becomes the lowest, and a pure white copy of the background part is created.''

When a copying machine product is shipped, it is adjusted so that the background part is reproduced as pure white, or in other words, the background part is adjusted so that no stains or smudges occur.However, as the machine is used, Gradually, background stains begin to occur.This is due to deterioration of the exposure optical system of the copying machine, deterioration of the photoconductor strength, and deterioration of the developer.For example, ■
As shown in the quadrant, when the optical system deteriorates, the amount of exposure to the photoreceptor decreases even if the original density remains the same, so the surface potential of the photoreceptor increases and the density of the developed image increases. Further, as shown in quadrant (2), when the photoreceptor deteriorates, the surface potential of the photoreceptor increases even with the same amount of exposure, and the density of the developed image increases.

Furthermore, as shown in quadrant (2), when the developer deteriorates, the density of the developed image increases even if the surface potential of the photoreceptor remains the same.

Therefore, when these deteriorate, the background portion, which was reproduced as pure white in the initial stage of use, becomes smudged.

From the above relationship, when background stains occur on copies, the first step is to lower the surface potential of the photoreceptor in the background area. Conventionally, this has been accomplished by increasing the amount of exposure using an aperture dial provided on the operation panel of the copying machine. However, since background smudges occur due to the various causes mentioned above, the aperture dial, which has a wide adjustment range, was originally used to adjust the copy density for originals with different densities.
It is difficult to adequately prevent dirt and rain. Furthermore, since the adjustment position and adjustment range change due to deterioration in other parts, it is not always possible to obtain a good copy at that position after adjustment.

Another technique for preventing background smearing is a technique for increasing the developing bias voltage. This is achieved by applying a developing bias voltage slightly higher than the surface potential of the photoconductor to a conductive member, such as a developing roller, that carries developer close to the surface of the photoconductor in the developing device. This is a technology that prevents developer from adhering to the background. Therefore, even if the surface potential of the photoreceptor increases, background smear can be prevented by adjusting the bias voltage higher than this. However, if the bias voltage is set too high, image areas of low-density originals or low-contrast originals will also disappear, making it impossible to reproduce them.

If the background smear prevention IE by adjusting the exposure amount and developing bias value is performed while looking at the finished copy, the copy will be wasted. Conventionally, therefore, a technique has been proposed in which the average potential on the surface of the photoreceptor is detected and this is used as a parameter to automatically adjust the exposure amount or the developing bias voltage value to an appropriate value. However, in addition to the problem of increasing the size and cost of the device due to the electrometer being installed, it not only lacks reliability because it requires maintenance, but also makes it impossible to detect deterioration of the developer, so total control is limited. As a system, it is incomplete. For this reason, in the past, periodic maintenance work such as cleaning and replacement of each unit was unavoidable, and the resulting cost increase was a problem that could not be ignored.

(Objective of the Invention) Therefore, the object of the present invention is to eliminate the need for the user to adjust the exposure amount by adjusting the aperture dial, that is, even if the aperture dial is always in the same position, or ultimately without the need for an aperture dial. An object of the present invention is to provide an improved electrophotographic image control method that can always obtain good copies without background smudges.

A further object of the present invention is to reduce the total cost by not requiring much maintenance related to image control, and even if it does, it is possible to perform efficient maintenance work by instructing the timing and location of maintenance. An object of the present invention is to provide an image control method.

This invention was made by focusing on the fact that background smudges due to deterioration of various units occur noticeably in low potential areas such as non-image areas or background areas of the photoreceptor surface potential. The source is irradiated on the low potential surface on which a small amount of toner adheres, and on the reference potential surface where there is little or no toner adhesion, and the amounts of reflected light from each are compared with each other until the two match. That is, the exposure amount and/or developing bias voltage is increased until it is determined that there is no or almost no toner adhesion to the background area, and only when these upper limits are likely to be exceeded, a warning signal is issued to request maintenance.

Hereinafter, the configuration of the present invention will be explained based on embodiments.

(Structure of the Invention) First, as shown in the deterioration system characteristic curve, which is the theoretical basis of this invention, the photoreceptor characteristic curve in the ■quadrant, and the developer characteristic curve in the ■quadrant, we will explain the deterioration during the deterioration. The degree is δ1 in the high potential part
The focus is on the fact that δ2 is larger in the low potential area (the low concentration area in the ■ quadrant). In other words, in the ■ quadrant, when the original density is low, the exposure amount decreases greatly due to the deterioration of the optical system; The density of the developed image increases greatly in low potential parts of the body due to developer deterioration.

Therefore, if an increase in the density of the developed image in the low potential area of the photoconductor, that is, a background stain, is detected quickly, deterioration of the optical system, photoconductor, developer, etc. can be detected quickly, and based on this, the exposure amount can be determined. By increasing the value or developing bias voltage, good copies without background smudges can always be obtained.

Detection of background stains is performed using a light emitting diode LED, a variable resistor R1, and a phototransistor P as shown in FIG. 2, for example.
This is carried out using a photosensor unit consisting of a combination of a transistor and a dividing resistor R2. When the surface of the photoconductor is irradiated by a light emitting diode LED and the reflected light is received by the phototransistor PTr, if toner is attached to the surface of the photoconductor, the amount of reflection 'yfS is small, so the current flowing to the phototransistor PTr is is also small, and vice versa it becomes large. Therefore, since the output of the photosensor is proportional to the developed image density, as shown in quadrant 2 of FIG. 1, when the sensor output decreases, it is possible to detect that the developed image density has increased.

This invention uses such a photosensor unit to detect the amount of light reflected from the surface of the low potential part of the photoreceptor,
By comparing this with the amount of reflected light from the surface of the base potential part with no or almost no toner adhesion, the degree of scumming on the surface of the low potential part is detected, and if there is scumming, that is, the two force measurement values are different. To prevent background smearing, increase the developing bias voltage and/or exposure amount so that both of them match, and only when the increased amount reaches the specified upper limit, call a service person and remove the parts. Perform maintenance such as replacement and repair.

FIG. 3 schematically shows an example of an electrophotographic copying machine to which the method of the present invention is applied. A charging charger 2, an erase lamp 3, a developing device 4, a photosensor unit 5, a transfer charger 6, a separation charger 7, a separation claw 8, a cleaning device 9, a static elimination lamp 10, etc. are arranged around the photosensitive drum 1. There is. Above the photosensitive drum 1, a document table glass 12 for placing a document 11 is arranged horizontally, and below it, an exposure system consisting of a mirror 13, a lens 14, a mirror 15, etc. is arranged. There is.

A photosensitive drum 1 is mounted on one end of the document platen glass 12.
A detection pattern 16 with a density of about 01 to form a low potential surface on the surface is held by a 1" second metal plate 17.

When the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the charging charger 2, and then the erase lamp 3 erases the charged charges on the portion of the original 11 other than the size, the image of the original 11 is exposed to light through the lens 14 etc. It is projected onto the surface of the body drum 1. As a result, the charges on the photoreceptor drum 1 are selectively erased according to the brightness of the document sheet, and an electrostatic latent image corresponding to the document image is formed thereon. This electrostatic latent image is developed by being supplied with developer from a rotating developing roller 18 holding developer in the developing device 4 . Development is performed by toner stirred in a developer being triboelectrically charged to have a polarity opposite to that of the electrostatic latent image and electrostatically adhering to the latent image. The toner image on the photoreceptor drum 1 obtained by development is overlapped with a transfer paper 19 that is sent in synchronization with this image formation, and the transfer paper 19 is superimposed on the toner image on the photoreceptor drum 1 obtained by the development, and the By being charged, the toner image is transferred onto a single transfer paper.The transfer paper 19 is then subjected to charge removal by the separation charmer 7, and the separation claw 8
The photoreceptor is separated from the surface of the photoreceptor drum 1 and directed to a fixing device (not shown). One of the photosensitive drums 1 has toner remaining on its surface removed by a cleaning device 9, and the remaining potential is erased by a static elimination lamp 10.

The above is a normal copying process, but when carrying out the method of the present invention, only the cover for holding the original is placed on the original glass table 12 without placing the original 11, and the normal copying process is performed. Performs only charging, exposure, development, cleaning, and static neutralization. As a result, an electrostatic latent image corresponding to the detection pattern 16 is formed on a portion of the surface of the photoreceptor drum 1, and this is developed by the developing device 4. Since the density of the detection pattern 16 is very low at 01, the latent image corresponding to the detection pattern 16 has a low potential and a very small amount of toner adhesion, and constitutes the surface of the low potential portion in the present invention. On the other hand, the surface of the photosensitive drum 1 other than the portion corresponding to the detection pattern 16 is exposed to white light because the back side of the document holding cover is white, and its surface potential is even lower than that of the portion corresponding to the detection pattern. There is no or almost no carbon, and it constitutes the surface of the reference potential portion in this invention. Of course, this area is attached to the non-image area or background area of the original, so if the back of the original holding cover gets dirty or the valley unit deteriorates, toner will adhere there and cause background smudges. In this embodiment, since the surface of the photoconductor is detected in its best condition with no deterioration in the troughs at the time of shipment from the copier, there is no toner adhesion, and this is therefore stored in the microcomputer and used as a reference from then on. Use as value.

Two areas on the surface of the photoreceptor drum 1 formed in this manner, namely, the surface of the low-potential area with a small amount of toner adhesion corresponding to the detection pattern 16, and the surface of the low potential area where a small amount of toner adhesion corresponds to the detection pattern 16 are irradiated with light from the toner adhesion source 5 and measured. Reduce. Each measured value (good, about 11 by dividing resistors 20 and 21)
5 and is input to the control circuit 23 via the A/D converter 22. In this control circuit 23,
It is judged whether these two input values are the same value, and if they are the same value, that is, there is no increase in the amount of toner adhesion on the surface of the low potential part, then leave it as is; if they are not the same value, that is, there is an increase in the amount of toner adhesion on the surface of the low potential part. In this case, the developing bias power supply 24 is driven by a signal from the control circuit 23, and the developing bias voltage applied to the developing roller 18 of the developing device 4 is 1.
Increased by steps. Such an operation is repeated within a certain limit until the two detection signals become the same value, and if the limit is about to be exceeded, a warning signal is issued and the system is inspected and adjusted by a service person.

The operation in the control circuit 23 is performed using the well-known CPU, ROM, RAM, and IF incorporated in recent copying machines.
FIG. 4 shows an example of the program.

First, when the copy switch is turned on, the number of copies is 1000.
It is determined whether it is the 1st copy, and if it is less than 1000,
Normally, there is no background smudge, so copying is performed using the initially set bias. 1000
At the time of the first sheet, the light emitting diode LED of the photo sensor unit is turned on to detect the amount of toner adhesion on the surface of the low potential part of the photoconductor, and compare it with the amount of toner adhesion on the surface of the reference potential part stored in RAM. and if they are equivalent, take a copy with the same bias. If it is a true value, when no copying operation is being performed, it is first determined whether the developing bias is at its upper limit, the 6th step, and if yes, a serviceman call will flash and a serviceman call will be sent. inspect and repair and readjust the bias. If no, increase the bias by one step, take a copy, detect the amount of toner adhesion on the surface of the low potential part again, and repeat the same operation until the same value is reached.

The developing bias is 7 from the zero step to the 6th step.
In the step A and zero step, the best bias voltage is set at the time of shipment of the copying machine, and then the bias voltage is increased by 30 V per step until the fifth step, where the bias voltage can be changed to 150 V. If the bias voltage is increased beyond this level, there will be problems in terms of electrical safety, carriers in the developer will land on the surface of the photoreceptor, and low-contrast originals may not be reproduced, so this is the upper limit. It is stipulated that When the sixth step, which is the upper limit, is reached, copying continues at the fifth step (7') bias voltage, during which maintenance is performed by a serviceman. When the two detection signals match by adjusting the bias, or when the serviceman readjusts the bias, the counter that counts the 1000th copy is reset, and development is performed with that bias until the next 1000 copies. As an alternative to this bias control, the exposure amount may be controlled, or the exposure amount may be controlled first and the bias control may be performed when the exposure amount is out of that range. In the latter case, the control range becomes even wider, so the interval between maintenance becomes longer. The exposure amount is controlled by changing the aperture or changing the voltage of the exposure lamp.

The first detection is performed in an unused state when the copier is shipped or before the first copy after being delivered to a user. As shown in FIG. 5, first, the light emitting diode LED of the photosensor unit is turned on at time t1, and at the same time, all of its output signals are input to the A/D converter 22 and the control circuit 23, and the light emitting diode LED It continues until it turns off at time t2. During this time,
The time is sufficient to detect the amount of toner adhering to the surface of the low potential portion and the surface of the base potential portion on the photoreceptor, and consideration is given to prevent variations in control. In the control circuit 23,
As mentioned above, the measured values of the surface of the low potential part and the reference potential part are memorized, and the measured value of the reference part is constantly compared with the new measured value of the low potential part that comes in each time, and when it is full, it is memorized. Previous data is sequentially output. Synchronization is performed by synchronization circuits that sample different data.

The low potential portion and the reference potential portion may be provided on the surface of the photoreceptor drum 1 in a non-image forming area at the end of the photoreceptor drum 1 as shown in FIG. 6, or as shown in FIG. It may also be an image forming area. Reference numeral 25 is the surface of the low potential portion, and 26 is the surface of the reference potential portion. Reference numeral 5 is a photosensor unit.

When the detection section is provided within the image forming area as shown in FIG. 7, it is necessary to set the image forming timing so that the pattern on the low potential section surface 25 is not transferred to the transfer paper during normal copying. .

In the above embodiment, the portion of the detection pattern 16 on the surface of the photoreceptor drum 1 where no corresponding image is formed was used as the reference potential portion, but the detection pattern 16 on the platen glass 12
White reference patterns may be arranged next to each other to form a detection pattern corresponding low potential section 25 and a reference pattern corresponding reference potential section 26 on the photosensitive drum 1, as shown in FIG. .

In addition, in order to provide such a pattern on the document platen glass 12, the non-image forming area 1a of the photoreceptor drum 1 is made insulating and separate from the photoreceptor drum 1, and a conductive mirror-finished area is provided thereon. A reference potential section 26 and a low potential section 25 formed of the same photoconductive material as the photoconductor drum 1 may be provided. Since this reference potential section 26 is conductive, no potential is applied even if it is exposed to charging, and because it has a mirror finish, it is difficult for toner to adhere to it, and it acts as an absolute reference surface that will always be free from toner adhesion even if various parts deteriorate. do. One of the low potential portions 25 corresponds to the reference potential portion in the above embodiment, that is, the background portion of the photoreceptor, and its potential increases due to deterioration of each portion, and becomes an indicator of occurrence of background smudge.

In the above case, the non-image forming area 1a is an extension of the photoreceptor drum 1, that is, it is made of the same material, and the absolute reference plane 26 as described above is provided therein insulated from the surroundings, and the low potential area 2
5, the background portion of the photoreceptor drum 1 may be used as is. In addition, the low potential portion 25 may include an area on the surface of the photoreceptor drum 1 that is not charged by the charger 2, or an area where the charged charge is erased by the erase lamp 3 even if it is charged by this. can be used.

Further, as shown in FIG. 9, such an absolute reference plane 26
is provided near the surface of the photoreceptor drum 1, and a photosensor unit 5 is provided rotatably around a vertical axis to sequentially detect this absolute base surface 26 and the background portion 25 of the photoreceptor drum 1. It's okay. In this case, since the reference pattern is provided completely independently of the original exposure optical system, it is easy to control the detection timing, etc.

Furthermore, the same surface of the photosensitive drum 1 can be used as both the low potential section and the reference potential section without using any of the detection patterns or reference patterns as described above. That is,
When detecting a low potential area, the surface of the photoreceptor is charged, exposed to white light, and developed. When detecting a reference potential area, the surface of the photoreceptor is charged, exposed, and not developed. Detect the surface.

(Effects of the Invention) As described above, according to the method of the present invention, the amount of toner adhesion on the low potential surface of the photoconductor, where the occurrence of scumming due to deterioration of various parts is most noticeable, and the amount of toner adhesion on the low potential surface of the photoconductor, and the amount of toner adhesion on the low potential surface of the photoconductor, where the occurrence of background smearing due to deterioration of various parts is most noticeable, can be reduced. It detects the amount of toner adhering to the reference potential surface, compares it with each other, and automatically adjusts the development bias and/or exposure amount to match the two to prevent background smearing, so the configuration is simple and maintenance intervals are long. Highly reliable image control becomes possible.

[Brief explanation of drawings]

Fig. 1 is a graph showing general characteristics of each part in an electrophotographic process, Fig. 2 is an electric circuit showing an example of a photosensor unit used in the present invention, and Fig. 3 is an electronic FIG. 4 is a schematic configuration diagram showing an example of a photocopier; FIG. 4 is a flowchart showing -fl of a program in the control circuit of the invention; FIG. 5 is a timing chart showing an example of detection timing in the control circuit of the invention 6 to 9 are schematic illustrations of photoreceptor drums showing various aspects of the sensing surface of the present invention. DESCRIPTION OF SYMBOLS 1... Photosensitive tram, 5... Photo sensor unit, 16... Detection pattern, 25... Low potential part surface, 26... Reference potential part surface. Figure 5 Figure 6 475-

Claims (1)

[Scope of Claims] Light is irradiated onto the surface of a low-potential portion to which a small amount of toner sticks during development and the surface of a reference-potential portion where toner is not or hardly adhered, and the amount of reflected light from each portion is detected. , mutually comparing the detection value from the surface of the low potential part and the detection value from the surface of the reference potential part, and when the two horizontal output values do not match, the developing bias voltage value and/or and increasing the exposure amount.